1. Field of the Invention
The present invention generally relates to an antenna device, and more particularly, to an improvement of a microstrip antenna incorporated with an electronic circuit.
2. Description of the Related Art
Conventionally, there has been known a microstrip antenna in which an electronic circuit such as an amplifier, filter or the like is incorporated (referred to as an antenna device hereinafter).
In a known antenna device as shown in FIGS. 19 and 20 (referred to as a first prior art hereinafter), a microstrip antenna and an electronic circuit to be connected therewith are piled one upon another in a vertical direction.
More specifically, the antenna device of the first prior art in FIGS. 19 and 20 generally includes a dielectric substrate 1 in a circular flat plate-like configuration, a circular radiation electrode 2 formed at a central portion on one main surface of said dielectric substrate 1, a circular ground electrode 3 formed on an entire face of the other main surface of said dielectric substrate 1, and a feeder line 4 connected at its one end 4a to said radiation electrode 2 for supplying power thereto, and provided in a position somewhat deviated in a direction of diameter from a center of the radiation electrode 2.
In the above arrangement, the so-called microstrip antenna is constituted by the dielectric substrate 1, radiation electrode 2, ground electrode 3, and feeder line 4. This microstrip antenna is fixedly placed on a base 5 made, for example, of a metallic conductor. On an under surface of the base 5, an electronic circuit 6 having an amplifier, filter or the like is fixedly mounted. The electronic circuit 6 generally includes an insulative circuit substrate 6a, a ground electrode 6b formed on one main surface of the circuit substrate 6a, a circuit pattern 6c and electronic parts (capacitor, resistor, etc.) 6d formed on the other main surface thereof.
The feeder line 4 referred to earlier extends through the radiation electrode 2, dielectric substrate 1, ground electrode 3, base 5, ground electrode 6b, and circuit substrate 6a, with the other end 4b thereof being connected to the circuit pattern 6c formed on the other main surface of the circuit substrate 6a. In other words, power is given to the feeder line 4 through the circuit pattern 6a.
Moreover, on the under surface of the base 5, a cap member 7 is provided for protecting the electronic circuit 6, and preventing electromagnetic wave noises.
In another example of conventional antenna devices as shown in FIGS. 21 and 22 (referred to as a second prior art hereinafter), the microstrip antenna and the electronic circuit connected thereto are aligned laterally on the same dielectric substrate.
More specifically, as shown in FIGS. 21 and 22, on one main surface of a dielectric substrate 11 in a rectangular flat plate-like shape, a circular radiation electrode 21 is formed at a central portion in the left half portion thereof, while an electronic circuit 61 is constituted at a central portion in its right half portion as shown, with the radiation electrode 21 and the electronic circuit 61 being connected to each other by a feeder line 41. Moreover, on the other main surface of the dielectric substrate 11, a ground electrode 31 is formed on its entire surface.
In the antenna device of the first prior art as described earlier, since the microstrip antenna and the electronic circuit 6 are piled up vertically one upon another, the antenna device tends to be higher on the whole, and thus, the advantage of the microstrip antenna which is thin is undesirably lost.
On the other hand, in the antenna device of the second prior art technique also referred to above, although the arrangement may be formed to be thin, since the microstrip antenna and the electronic circuit 61 are disposed on the same plane, there is involved another problem that the planner shape tends to be large.